Flexible insulation is formed on wire and cable products by use of flexible base polymers such as ethylene-propylene-diene terpolymer, also known as EPDM. This EPDM is the ASTM designation for an ethylene-propylene terpolymers or a quatrepolymer. Two such quatrepolymers are the polymer products sold commercially as Nordel 2722 of DuPont and Nordel 2522 of DuPont. Other ethylene-propylene copolymers, terpolymers and quatrepolymers may be used in place of the specific EPDMs such as the Nordel 2000 Series of DuPont. Further illustrations of ethylene-propylene polymers which have been used in flexible insulation for wire and cable include the Vistalon 404 of the Exxon Chemical Americas Company, which is an ethylene-propylene copolymer. Further, the Nordel 1040, for example, and Nordel 1145 of the DuPont Company have been employed in making flexible wire insulation for wire and cable products. These latter DuPont products are ethylene-propylene terpolymers.
The above and similar flexible polymers compositions have been incorporated as the base polymer of flexible wire insulation. Such flexible wire insulation has been used in the temperature ranges of a 90.degree. C. wire rating, and a 105.degree. C. wire rating and some of them up to a 125.degree. C. wire rating, according to applicable UL standards. One of the problems which such compositions encounter as the compositions are employed at higher temperatures, is that there is a tendency for the compositions to discolor. In other words, as a generality, the compositions of flexible wire insulation which have the ethylene-propylene copolymer, terpolymer or quatrepolymer bases do have a tendency to discolor as the temperature of use or temperature of test of the compositions is raised. This tendency is present even though the compositions themselves may have some ingredients which permit them to be used at more elevated temperatures. For example, the composition of U.S. Pat. No. 4,125,509 does have substantial resistance to discoloration at relatively short test periods of about five hours. The composition of the U.S. Pat. No. 4,125,509 patent does have deteriorating properties when operated continuously at a 150.degree. C. range even though it does not discolor for short periods at this temperature.
As a general rule, it is desirable for a composition to have relatively high temperature operating capability without serious impairment of the performance characteristics of the insulation and without serious color changes. Some color changes are not associated with deterioration of performance characteristics but the end user or customer of the product may associate performance characteristic changes with the changes in color and, accordingly, from a customer's point of view, it is desirable that color deterioration be avoided where feasible.
It has now been discovered that through a relatively minor change in the composition of a flexible wire insulation material that the tendency toward discoloration of the composition from test or use at elevated temperatures can be inhibited and further that, in some instances, the avoidance of color deterioration can be accompanied by improved properties.